This invention relates to a throttle valve control apparatus for use with an internal combustion engine having a throttle valve and, more particularly, to such an apparatus for detecting a failure of a return spring used to urge the throttle valve in an opening or closing direction.
Traction control apparatuses have been proposed to control the engine output so as to hold a slip factor within a predetermined range when slip occurs for the vehicle drive wheels. The engine output control is made by controlling the position of a throttle valve located in an air induction passage for controlling the amount of air permitted to enter the engine. For this purpose, the traction control apparatus produces a required throttle valve position for an electronic control unit which compares it with a detected throttle valve position to provide a closed loop control signal in response to a sensed deviation of the detected throttle valve position from the required throttle valve position. The closed loop control signal is used to drive a throttle valve actuator so as to move the throttle valve in a direction zeroing the sensed deviation.
The traction control apparatus is applicable to a single throttle structure having a single throttle valve located within an engine induction passage and also to a tandem throttle structure having main and auxiliary throttle valves located in series within an engine induction passage. The main throttle valve is connected through a mechanical linkage to an accelerator pedal and the auxiliary throttle valve is connected to a throttle valve actuator controlled by the electric control unit.
For such a single throttle structure, the electric control unit normally controls the throttle valve in response to a change in the position of an accelerator pedal and in response to the required throttle valve position fed from the traction control apparatus when slip occurs for the vehicle drive wheels. For such a tandem throttle structure, the electric control unit normally controls the throttle valve actuator to hold the auxiliary throttle valve in its fully-open position and controls the throttle valve actuator to move the auxiliary throttle valve in a closing direction when slip occurs for the vehicle drive wheels.
Normally, a return spring is used to urge the throttle valve in a closing direction for the single throttle structure and to urge the auxiliary throttle valve in an opening direction for the tandem throttle structure. The control unit employs the return spring to move the throttle valve to a fail-save position in the event of failure of the components used for the throttle valve control. In the event of failure of the return spring itself, however, the fail-safe operation will be invalid. There have been proposed no means for detecting a failure of the return spring in spite of the fact that it is very difficult to check the failure of the return spring from the operation of the throttle valve.